Fibrous organic insulating webs are known in the art. The synthetic polymeric materials typically comprising the fibers of such webs are generally relatively weak absorbers of infrared radiation. Consequently, webs in the past have primarily relied upon immobilized air to reduce heat transmission and thereby increase their insulating qualities. However, the insulating value of still air trapped between the fibers of such a web is limited due to the transmission of heat via radiation. Providing an air space within the individual fibers so as to make them hollow only modestly increases the effectiveness of blocking the infrared radiation heat transfer.
It has now been discovered that the insulating effectiveness of a web is significantly increased when polymeric fibers are incorporated into the web which contain an effective infrared absorbing amount of an infrared absorbing additive such as graphite. Such fibers are believed to be rendered substantially opaque to the infrared heat radiation such that they effectively block the radiation heat transfer through the web thereby decreasing the thermal conductivity and increasing the insulating value of such webs.
It has been found that webs containing the opacified fibers of the instant invention demonstrate significantly lower thermal conductivity values than webs at the same loft made of the same intimately blended fibers, but without an infrared opacifying additive. This translates into higher insulating values which means that the webs of the instant invention are substantially warmer than webs of conventional technology. Consequently, it is expected that these webs will find particular utility as fiberfill insulation especially in wearing apparel, sleeping bags and the like.